The invention is based on a high-voltage insulator for installation in chambers carrying a gas highly charged with solid particles, especially chambers carrying an exhaust gas deriving from internal combustion engines. A high-voltage insulator of this kind is known, for instance from U.S. Pat. No. 2,565,458, and is used there in an electrostatic filter by means of which small foreign particles such as dust are to be removed from gases similar to air. These particular high-voltage insulators used are basically columnar in structure, with annularly extending ribs, and they serve to retain the precipitator plates, which are exposed to high voltage, in the interior of the housing. Such insulators, because of the manner in which they are used, are exposed to dirty gas and can easily become covered with a layer of dirt. The threshold for igniting partial discharges on the surface is lowered to a greater or lesser extent, depending on the composition of this layer of dirt. Leakage currents, causing permanent power losses on the part of the electric supply device for the electrostatic filter, flow via a conductive layer of foreign material. Such filters are also used for filtering out foreign bodies such as soot from the exhaust gases of internal combustion engines. Especially in self-igniting engines, the exhaust gases often contain a rather large amount of very finely dispersed soot. This soot quite quickly forms a continuous layer of uniform thickness on the insulators exposed to the exhaust gas atmosphere, and it has the property of being a relatively good conductor of electricity. Electric shunting via the insulators thus usually occurs very quickly, and this puts a considerable load on the means used for supplying high voltage to the electrostatic filter. Especially when electrostatic filters are used for internal combustion engines in motor vehicles, the high-voltage system for supplying voltage to the filter should be capable of operating for long periods virtually without shunting, if possible, and with the smallest possible losses of high-voltage power. The power loss or operating output of the electrostatic filter represents a reduction of the power provided to the vehicle by the engine. Excessively high power loss via the insulators would accordingly cause an undesirable increase in fuel consumption during vehicle operation.
While the partial discharge occurring via a continuous layer of dirt on the insulator surface is not extremely disadvantageous in motor vehicle high-voltage systems, under some circumstances the power losses caused by leakage currents may cause the total failure of the high-voltage system, if the power losses are on the order of magnitude of the total high-voltage power that is available. The partial discharges normally occur only briefly, because the voltage surges that then occur, which are dictated by the limited capacity of the vehicle high-voltage system, disrupt the discharges once again.
Accordingly, where an electrostatic filter is used to remove soot from Diesel exhaust gases, the known insulators discussed at the outset above would rapidly destroy the functional capacity of the high-voltage supply system, because a conductive soot burning layer that is several millimeters thick can form on the insulators after only a few hours of operation.
Another electrostatic filter for cleaning internal combustion engine exhaust gases is known from British Pat. No. 1,022,714, in which the problem of soot contamination of the insulator that supports the electrodes is supposedly solved, but in a rather complicated manner. In the soot filtering device known from this patent, axial electrodes are provided inside a tube carrying an exhaust gas, and each of the electrodes is retained at the ends of this tube by two insulator parts. One of these insulator parts is bell-shaped and joined to the housing of the scrubbing system, while the other insulator part is disc-shaped and porous. A chamber which is exposed to compressed air through the electrode inlet is enclosed between the disc-shaped insulator part and the bell-shaped insulator part. The disc-shaped insulator part is immediately adjacent to the soot-charged atmosphere in the interior of the apparatus and is supposed to be kept free of soot by having the compressed air blown through its pores into the interior of the apparatus. This apparatus is rather complicated, and furthermore this design results in rather large structural sizes, because the second insulator part for voltage insulation of a magnitude of for instance 20 kV must necessarily have a large diameter.